This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Nitric oxide (NO) plays key roles in various physiological processes including neurotransmission, blood pressure regulation and the immune response. NO modifies proteins by binding to metals and cysteine thiol groups (S-nitrosation) to modulate enzyme activity, localization, and association with other proteins. Importantly, S-nitrosation of cysteines plays key roles in vascular homeostasis. HNO, a reduced congener of NO, also modifies cysteine thiols and is a potential therapeutic agent for heart failure. The mechanism by which nitrogen oxides, both NO and HNO, regulate protein function is largely unknown. Therefore, to clarify central roles for NO and HNO in biology roles, this proposal addresses the following questions: 1) What is the mechanism for NO-induced activation of cGMP production by soluble guanylate cyclase (sGC)? 2) What is the structural basis for allosteric NO and HNO modifications that affect protein activity, protein-protein association, and signal transduction? These structural analyses will provide a powerful molecular framework for the design of novel small molecules compounds for the treatment of hypertension, heart failure, atherosclerosis, diabetes, metabolic syndrome, and vascular disorders (Alzheimer?s disease) with neurodegenerative consequences.